import java.security.Key;

public class MyLinkedList {
    static class ListNode {
        public int val;
        public ListNode prev;
        public ListNode next;

        public ListNode(int val) {
            this.val = val;
        }
    }

    ListNode head = new ListNode(-1);
    ListNode last = new ListNode(-1);

    public void creatList() {
        ListNode node1 = new ListNode(12);
        ListNode node2 = new ListNode(23);
        ListNode node3 = new ListNode(34);
        ListNode node4 = new ListNode(45);
        ListNode node5 = new ListNode(56);

        head.next = node1;
        head.prev = null;
        node1.prev = head;
        node1.next = node2;
        node2.prev = node1;
        node2.next = node3;
        node3.prev = node2;
        node3.next = node4;
        node4.prev = node3;
        node4.next = node5;
        node5.prev = node4;
        node5.next = null;
    }

    //得到单链表的长度
    public int size() {
        ListNode cur = head;
        int count = 0;
        while (cur != null) {
            count++;
            cur = cur.next;
        }
        return count;
    }

    public void display() {
        ListNode cur = head;
        while (cur != null) {
            System.out.print(cur.val + " ");
            cur = cur.next;
        }
        System.out.println();
    }

    //查找是否包含关键字key是否在单链表当中
    public boolean contains(int key) {
        ListNode cur = head;
        while (cur != null) {
            if (cur.val == key) {
                return true;
            }
            cur = cur.next;
        }
        return true;
    }

    //头插法
    public void addFirst(int data) {
        ListNode node = new ListNode(data);
        if (head == null) {
            head = node;
            last = node;
            return;
        }
        node.next = head;
        head.prev = node;
        head = node;
    }

    //尾插法
    public void addLast(int data) {
        ListNode node = new ListNode(data);
        if (head == null) {
            head = node;
            last = node;
            return;
        }
        last.next = node;
        node.prev = last;
        last = node;
    }
}
